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What is PZEV in Cars?

By Autolist Staff | March 21, 2019

What Does PZEV Mean?
PZEV stands for “Partial Zero-Emissions Vehicle", an administrative category of low-emission vehicles.

The PZEV designation was a compromise between automakers and the California Air Resources Board (CARB) in 1998 as a way to postpone the state-imposed production of zero-emission vehicles (ZEV) powered by alternative fuel sources like electric batteries and hydrogen fuel cells.

CARB introduced the ZEV standard all the way back in 1990, but the cost of forcing electric vehicles and those powered by fuel cells wasn't possible at the time. PZEV technology was introduced as a short-term solution while car manufacturers gradually improved their alternative fuel vehicles.

PZEVs use normal internal combustion engines and produce zero evaporative emissions. PZEV engines still burn gasoline and drive like ordinary, non-PZEV engines, thus emitting greenhouse gases, but they minimize local smog problems.

Compared to other emissions standards categories, PZEV vehicles are cleaner than Super Ultra Low Emission Vehicles (SULEV), Ultra Low Emission Vehicles (ULEV) and Low Emission Vehicles (LEV).

Advanced Technology Partial Zero Emission Vehicles (AT PZEVs), such as hybrid-electric cars and plug-in hybrid electric vehicles (PHEVs) have stricter standards than PZEVs and are the next evolutionary step towards a true zero-emission vehicle. However, PHEVs and AT PZEVs still partially run on gas.

PZEVs were initially only available in the six "clean car states" (California, Maine, Massachusetts, New York, Oregon, Vermont) and Canada. A slew of other states (Alaska, Connecticut, Maryland, New Jersey, Pennsylvania, Rhode Island, and Washington ) followed suit soon after.

CARB encouraged PZEV production by issuing ZEV credits to car manufacturers for each such vehicle they sold in proportion to their annual auto sales in California. Without the necessary ZEV credit balance, car manufacturers cannot sell any vehicles in California. Surplus ZEV credits can be sold to manufacturers that are short on credits. The system has proven to be quite effective, as zero automakers have failed compliance.

Subaru was one of the first car manufacturers to ride the new green wave but other automakers such as Mazda, Volkswagen, Honda and Ford hopped on the wagon shortly thereafter with their own PZEV models.

The California Air Resources Board maintains a database of all cars with EV, Enhanced AT PZEV, AT PZEV and PZEV designations on their website.

Under the Hood
Making PZEVs is a lot easier for auto manufacturers since they don't have to make drastic changes to a vehicle's design, such as allocating space for a large set of batteries like on an EV or revamping a car's suspension to accommodate wheel-hub electric motors.

Since PZEVs run on conventional vehicle platforms, with internal combustion engines and standard transmissions, the modifications mainly target fuel vapor off-gassing by modifying a vehicle's fuel system and swapping in a more robust catalytic converter.

PZEVs are equipped with three unique components in their fuel systems.

Anti-permeation fuel systems liners are layers of polymers that prevent gas vapors from leaking when vehicles are not in use. Vehicles have canisters of carbon between the gas cap and gas tank to capture gas vapor released from temperature swings or refueling before the gas reaches the outside air. The engine then sucks the fuel vapor into the combustion chamber, where it is promptly destroyed. Small amounts of vapor manage to bypass the primary canister, but PZEVs are outfitted with a carbon canister scrubber that traps 95% of the residual vapor. Carbon air intake traps are honeycomb-shaped filters made from activated carbon or metal and zeolite, another porous mineral, that grabs remaining vapor from the combustion chamber and intake manifold after you turn off your vehicle's engine.

All fuel-powered cars use catalytic converters to turn toxic exhaust pollutants (carbon monoxide, nitrogen oxides, hydrocarbons) into less toxic chemicals (carbon dioxide, nitrogen, water), but PZEVs position two close-coupled catalytic converters nearer to the engine than standard cars. Catalytic converters contain small amounts of precious metals such as platinum, palladium, and rhodium, which are the active components for making vehicle emissions safer. Additionally, a car's emissions are dirtier when the engine is colder; close-coupled catalytic converters help get vehicle engines running at a cleaner, hotter temperature faster.

These modifications to PZEV cars fuel systems and engine exhaust reduce local emissions that cause smog and acid rain by a whopping 90% when compared to regular internal combustion engine cars.

PZEVs come with a 15-year/150,000 mile warranty on their emission-control systems. CARB requires car manufacturers to provide this warranty so that the emissions quality of your PZEV will not be diminished over time. There are no government-sponsored financial incentives for buyers of standard internal combustion PZEVs; certain manufacturers may offer factory-direct rebates from time to time but it is up to consumers to find deals. Tax credits, incentives and rebates for hybrids, plug-in hybrids, electric vehicles and fuel cell vehicles may be available at both a state and federal level, plus additional incentives for installing home charging stations and/or solar power to charge them. Plus, cleaner air and a healthier environment is something everyone can enjoy.

As emission standards continue to become more stringent, PZEVs will become more commonplace. The EPA passed the Tier 3 Vehicle Emissions Standards in 2014 and it was implemented in 2017. Under the new regulations, non-PZEVs will be gradually phased out of production and the redundant PZEV designation will be retired as it becomes the norm. All new vehicles sold in 2025 will effectively be PZEVs.

Hybrid-electric cars, which fall under the category of Advanced Technology Partial Zero Emission Vehicles (AT PZEVs) and plug-in hybrid electric vehicles (PHEVs) mark the next incremental step on the country's quest for emissions reduction and cleaner air quality, but their time is also limited. The California Air Resources Board and other regulatory bodies will maintain their role in guiding production trends. The agency already amended the ZEV credit system in 2018, with battery electric and fuel cell vehicles being allocated more credits than PHEVs, which still run partially on gas. The road to true ZEV dominance is certainly a long one, but the path seems clear.